1. Field of the Invention
The present device and method relate generally to accessing, draining, and monitoring the lymphatic system. This device can be used to treat volume overload in heart failure, pulmonary edema, after surgical procedures and in other disease states in which interstitial volume removal or lymphatic sampling are of use.
2. Description of the Related Art
Congestive heart failure affects 5.5 million Americans and is a leading cause of death in the U.S. Each year, over one million patients are hospitalized for heart failure and 90% of these are diagnosed with volume overload. Volume overload in patients with heart failure is an acute manifestation of a chronic decrease in cardiac performance such that the heart is unable to pump and circulate the volume of blood returning from the venous system. As a result, blood accumulates in the pulmonary and peripheral tissues. A common and potentially life threatening consequence of decompensated heart failure is pulmonary edema, which presents as shortness of breath and poor oxygenation, both indicative of fluid accumulation in lung tissues and small airways. If left untreated, patients are at risk for hypoxic arrest and death. Peripheral swelling and venous distension are also common, although not as life threatening.
In most cases, patients with this presentation are known to be suffering from a chronic heart condition and are taking prescribed diuretic medications to control their volume status. The sudden onset of volume overload is due to either a miscalculation in salt and fluid intake or poor medication compliance on the part of the patient, or a result of a worsening heart condition, renal impairment, or resistance to diuretic medications.
Once diagnosed, the initial therapy for volume overload in decompensated heart failure is intravenous diuresis. Despite the use of intravenous diuretics in 90% of overload patients, the average hospital admission time is 4.3 days and over half of those discharged will return within six (6) months with the same diagnosis. It is suggested that the high readmission rate is due to inadequate volume reduction during their previous admission. Furthermore, approximately 30% of chronic heart failure patients on diuretics will develop resistance or renal failure as a result of their medication and require more invasive and higher risk therapies to control their volume status. These interventions include mechanical ventilation with positive pressure, central venous ultrafiltration, or hemodialysis.
The physiology of pulmonary edema suggests fluid accumulation in the small airways is the direct result of increased hydrostatic pressure in the surrounding capillaries, which leak first into the interstitial space between the capillary bed and the airway. This extracellular space is composed of protein matrices and small lymphatic channels designed specifically to accommodate homeostatic changes in pressure by draining any excess interstitial fluid which is not immediately resorbed by the venous capillary bed. These lymphatic channels combine as they travel towards the neck, eventually forming one large channel called the thoracic duct. The thoracic duct rejoins the systemic venous system at the lymphovenous junction, near the confluence of the left internal jugular and subclavian veins. In the case of clinically significant pulmonary edema, the hydrostatic forces generated by a failing heart quickly overwhelm the lymphatic system and blood plasma overflows into the smaller airways. In this case, the lymphatic system is limited by volume capacity and higher than expected flow pressures generated by the venous system into which the thoracic duct is draining.
The human lymphatic system has been accessed previously for the purposes of sampling and draining lymphatic fluid to treat blood cancers, transplant rejection, pancreatitis and rheumatoid arthritis. These maneuvers have involved open surgery and acute cannulation of the thoracic duct in small numbers of patients with extracorporeal processing of lymphatic fluid. The majority of the fluid was returned to the patient after processing.
While the function and overloading of the lymphatic system in pulmonary edema is well documented, current therapies for volume overload focus on systemic pharmaceutical diuresis or direct drainage of the vascular compartment to filter and remove blood plasma. Therefore, there exists a need for a therapy to monitor and manage pulmonary and systemic volume overload by manipulation and drainage of the existing lymphatic system. Drainage of lymphatic fluid specifically from the thoracic duct can quickly reverse the interstitial fluid imbalance in the pulmonary tissues and offload a significant amount of peripheral volume. Furthermore, lymphatic fluid is pre-filtered and does not include red blood cells or platelets which need to be separated and returned to the patient in conventional hemodialysis and ultrafiltration.
Outside of heart failure, development of this device will provide a much needed tool to accelerate research and treatment in a range of related disease states such as cancer, HIV, organ transplant, and autoimmune disorders.
Interstitial fluid accumulation can become a critical issue in any post-operative patient and is especially concerning after heart surgery, when it is important to limit cardiac stress. In these critical care and post-surgical volume management situations, and at other times, thoracic duct drainage in at-risk patients can augment volume management and prevent overload.
Fluid in the thoracic duct contains a high percentage of circulating CD-4 lymphocytes, the target cell for HIV. In animal models, drainage and characterization of T-cells by thoracic duct drainage can answer some of the fundamental immunological questions about recirculating lymphocyte pools to help develop new vaccine and antiviral therapies.
An early method of immune suppression in organ transplantation was thoracic duct drainage. The open cannulation procedure and subsequent wound care was challenging and unsuccessful in many patients. Once immune suppressive medications became more effective, this approach was abandoned altogether.